1. FIELD OF THE INVENTION
The present invention relates generally to a fluorescent lamp, and particularly concerns a reflector type fluorescent lamp for optical apparatus such as a copying machine.
2. DESCRIPTION OF THE PRIOR ART
In recent years, fluorescent lamps are becoming to be used widely, not only for general purpose illumination source but also for light sources of various optical apparatuses. When the fluorescent lamp is used for the optical apparatus, since the area of the object to be illuminated by the fluorescent lamp is narrow in width, it is general that the illumination is controlled such that luminous intensity distribution of the fluorescent lamp is directed to one direction necessary for that purpose by converging the luminous flux. As one conventional example of controlling the luminous intensity distribution by the fluorescent lamp itself, a reflector type fluorescent lamp has been known, wherein reflection film is formed on the inside wall of the glass tube to make a certain angle with respect to its axis thereby forming a wide stripe shaped aperture and a fluoresceent layer is formed only on the reflection layer, or on the reflection layer and on the aperture region.
In order to improve illuminance on the object of the illumination, another constitution of reflector type fluorescent lamp has been proposed in the U.S. Pat. No. 3,442,582, wherein a reflection layer having two stripe shaped apertures of a larger angle and smaller angle with respect to axis of the lamp tube, and a fluorescent layer is formed only on the reflective layer, the two apertures being disposed opposite with respect to the axis, and the lamp tube is used by disposing one of the stripe shaped apertures onto the object to be illuminated and light reflected by the object is taken out through the other stripe shaped aperture.
The fluorescent lamp of the former art has a problem that when used as a light source for an optical apparatus such as the copying machine, a single fluorescent lamp of that type cannot serve both to illuminate the object document to be copied and to illuminate a drum of photosensitive material as an erasing lamp to erase electric charge at the same time, since the lamp tube has only one light emitting aperture and transmittance of light at the part of the reflector is very low in comparison with the aperture part. And the latter lamp tube also has a problem that the light illuminating the document to be copied is lowered due to light emissiion from two apertures since there are two apertures which have no fluorescent layer. Accordingly for each of the above-mentioned prior art fluorescent lamps, there is a necessity of an additional lamp, for instance, a cold cathode discharge lamp which is other than the above-mentioned main fluorescent lamp as the erasing lamp. And for such additional lamp there is a necessity of additional spaces and lamp circuit therefor, and as a result, the miniaturization of the optical apparatus or designing of a small power consumption apparatus is not provided thereby.